Rechargeable batteries are widely used in various electric devices, ranging from small devices such as cellular phones, tablet computers, portable media players, personal digital assistants (PDAs) or the like, to large devices such as electrical vehicles. For such electric, devices that are powered by rechargeable batteries, battery charger becomes an essential accessory.
Earlier generations of the rechargeable batteries are Nickel Cadmium batteries or Nickel Metal Hydride batteries. These types of batteries have already been replaced by Lithium batteries in the market today. Typical Lithium battery charging control is achieved by two functional circuits: a charging circuit and an overcharge protection circuit, which are implemented in the device such as a cellular phone. The charging circuit typically can detect a connection between the charger and the mobile device, and control the charging current to the battery. The charging circuit may also have a measuring circuit to gauge the battery level of the battery under charging. The overcharge protection circuit can regulate an instable voltage to protect the battery, and it can also disable the charging circuit to prevent the battery from being overcharged when the battery level reaches a predetermined level.
Until today, however, there is no existing charger that is designed to provide a convenient and safe charging process. Taking cellular phone as an example, people usually charge their cellular phones in the night before they go to bed and unplug the charger in the morning when they get up. At that time in the morning, the cellular phones may have been charged for a long time. For a legacy cellular phone that has no overcharge protection circuit, the battery may be overcharged. Even for a cellular phone that has an overcharge protection circuit built therein, although the overcharge protection circuit can disable the charging circuit to prevent the battery from being overcharged, the charger is always providing power to the charging interface of the cellular phone until it is unplugged. In other words, the charging circuit is always subject to a voltage, which may deteriorate the characteristics of the charging circuit and even shorten the life of the battery.
Accordingly, there is a need for methods and apparatus that are capable of avoiding overcharge of the rechargeable battery and preventing the deterioration of the performance of the charging circuit. Advantageously, the present invention can meet such need.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.